Actuator control device

ABSTRACT

A valve actuator control device adapted to control the position of a valve actuator by means of solenoid valves, in which if the actuator position deviates from a desired position, but remains within a predetermined distance from said desired position, the control device is adapted to only return the actuator to the desired position after a delay period, thereby to increase the life span of said solenoid valves.

BACKGROUND OF THE INVENTION

This invention relates to an actuator control device for use inparticular, but not exclusively, with a pneumatic actuator.

Pneumatic actuators are used to activate valves which control the flowof a substance through a pipe or the like. These actuators may bepositioned by means of a control device provided with solenoid valves.Many re-adjustments may be required to obtain a desired valve position,in particular if the desired position is not constant.

A typical electrically operated on/off solenoid valve has a life ofapproximately 50 million operations. In applications where the flowvalves need to be constantly moved, the solenoid valves can expire inless than 12 months.

There are alternative mechanical ways of operating an actuator, howeverthese are more expensive to manufacture and to purchase than thoseprovided with the above described solenoid valves.

The present invention is intended to overcome some of the aboveproblems.

SUMMARY OF THE INVENTION

According to the present invention an actuator control device is adaptedto delay actuator movement towards a desired position if the actuator'sactual position is within a predetermined distance therefrom.

Preferably the control device can delay actuator movement for a numberof different predetermined time periods, which correspond to a number ofsequential predetermined distances away from the actuator's desiredposition.

In one construction the predetermined delay periods decrease the furtheraway from the desired position the actuator is. Therefore, if theactuator is a long way from its desired position there will be a small,or no, delay before the actuator is moved, however, if the actuator isvery near to its desired position there will be a long delay before theactuator is moved.

The actuator can also be provided with two input signals, the firstbeing the desired actuator position, and the second being the actualactuator position. The desired actuator position can be set via acontrol means accessible by the system operator. Alternatively, thedesired position can be sent from another part of the plumbing of thesystem with which the actuator and valve is used, for example an activepressure monitoring means downstream of the flow valve. The actualactuator position can be provided by a potentiometer of a knownconstruction.

The sequential predetermined distances can each be 0.7 degrees wide. Thedesired actuator position can be a 0.7 degrees wide band, which isprovided with four further 0.7 degree bands on either side.

The predetermined delay periods can be 13 seconds in the first bandoutside the desired band, then 7 seconds, 4 seconds and 2 seconds.Therefore, when the actual actuator position is between 0.1 degrees and0.7 degrees outside the desired 0.7 degree wide band, according to thedifference between the two input signals, the control device will notmove the actuator for 13 seconds. When the actuator is between 0.8degrees and 1.4 degrees from the desired band, the delay is 7 seconds,and so on.

If the actuator's actual position changes to a different 0.7 degreesband during the delay period, the control device can be adapted tomodify the delay period to correspond to the new position.

Therefore, if the actuator is positioned according to a 7 seconds delay,but moves after 5 seconds to the 13 seconds delay band, the actuatorwill operate after a further 8 seconds. However, if the actuator ispositioned according to a 7 seconds delay, and moves after 5 seconds tothe 4 seconds delay band, the actuator will operate immediately, becausemore than 4 seconds have elapsed.

With this arrangement actuator movements which may not be effective dueto the actuator's constantly changing position are not made.

In one construction the actuator is provided with solenoid-valves. Theactuator can be a “spring return” actuator of any known type, in whichthe position of the actuator is controlled by an inlet solenoid valveand an exhaust solenoid valve which control a force which acts against areturn force, for example a spring. In an alternative construction theactuator can be a “double acting” actuator of any known type, in whichthe position of the actuator is controlled by a number of solenoidvalves adapted to control a force and a return force.

The actuator can be used to control a flow valve, the position of whichmay need to be constantly changed to maintain a constant output flow.

The present invention can be performed in various ways, but oneembodiment will now be described by way of example, and with referenceto the accompanying drawing, in which:

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a diagram displaying the features of an actuator controldevice according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1 an actuator control device 1 is provided with an electronicprogram 2 which is adapted to delay the movement of a spring returnactuator 3 to a desired position when the actuator's 3 actual positionis within a predetermined distance from the desired position.

The control device 1 is connected to the actuator 3, which is connectedto a flow valve 6.

The control device 1 is provided with a desired position input signal 4,and an actual position input signal 5. The actual position input signal5 is drawn from the actual position of the valve stem 7 inside theactuator.

FIG. 1 shows three potential actual position input signals, A, B, and C.

In use the system operator, or an active pressure monitoring meansdownstream of the flow valve, provides a Desired position input signal4. The Control device 1 then moves the actuator to that desiredposition, at which point the control device begins a timer.

If the actuator changes position by 1 degree, actual position inputsignal A is fed into the control device 1.

If after seven seconds the input signal A remains in the same 0.7degrees wide band between 0.8 degrees and 1.4 degrees, the controldevice 1 will operate the actuator 3 and attempt to move it back in linewith the desired position input signal 4.

However, if the input signal 5 changes to position B in less than 7seconds, the actuator 3 is not moved by the control device 2, as themovement is no longer necessary.

In the event that the input signal 5 changes to another position outsidethe desired 0.7 degrees band in less than 7 seconds the actuator willoperate according to the delay period corresponding to the new position.So, for example, if the actuator moves after 5 seconds to position C theactuator will operate immediately because more than 4 seconds havepassed.

In the event that the input signal 5 is outside all of the nine 0.7degree wide bands, there is no delay in operating the actuator 3.

Therefore, the control device operates the actuator, and the actuator'ssolenoid valves, far less than in a conventional arrangement.

It will be appreciated that the predetermined distances and delayperiods can be any desired amount, and are not restricted to those shownin FIG. 1.

Further, it will be appreciated that the present invention can also beused to control a double acting actuator provided with inlet solenoidvalves and exhaust solenoid valves. A single control device can beadapted to control these valves, operating a combination to move theactuator in one direction, and another combination to move it in theopposite direction.

It has been found that with the above program of delay sequences, thelife time of a typical solenoid valve in an actuator is extended by over10 times. It has been further found that the delay system incorporatedinto the above described system does not effect the flow of thesubstance through the flow valve to any appreciable extent

Therefore an actuator control device is provided which uses inexpensivesolenoid valves whilst giving long life and good control.

Although a preferred embodiment of the invention has been specificallyillustrated and described herein, it is to be understood that minorvariations may be made in the apparatus without departing from thespirit and scope of the invention, as defined by the appended claims.

1. A valve actuator control device adapted to control the position of avalve actuator by means of solenoid valves, in which if the actuatorposition deviates from a desired position, but remains within apredetermined distance from said desired position, the control device isadapted to only return the actuator to the desired position after adelay period, thereby to increase the life span of said solenoid valves,in which the predetermined distance is divided into a number ofsections, and in which a different delay period is applied when theactuator is positioned in each section.
 2. A valve actuator controldevice as claimed in claim 1 in which the control device comprises anelectronic program adapted to control the position of a valve actuator.3. A valve actuator control device as claimed in claim 1 in which thedelay periods decrease in duration as the distance between the desiredposition and the actuator position increases in size.
 4. A valveactuator control device as claimed in claim 3 in which the valveactuator provides a rotational movement, and in which the desiredposition is a point or a section in the actuator's range of rotationalmovement, and each section of the predetermined distance is a band ofrotational movement in either direction from the desired position.
 5. Avalve actuator control device as claimed in claim 4 in which the desiredposition is a 0.7 degree wide band within the actuator's range ofrotational movement, and each section of the predetermined distance is a0.7 degree wide band, and in which the predetermined distance is dividedinto four 0.7 degree wide bands.
 6. A valve actuator control device asclaimed in claim 5 in which the control device is adapted to delaymovement of the actuator to the desired position for thirteen secondswhen the actuator is positioned in the first 0.7 degree wide bandoutside the desired position, for seven seconds in the second band, forfour seconds in the third band and for two seconds in the fourth band,and in which when the actuator is positioned outside the predetermineddistance there is no delay in movement of the actuator to the desiredposition.
 7. A valve actuator control device as claimed in claim 6 inwhich if the actuator position changes from a first band to a secondband, and a first delay period changes to a second delay period, thetime which elapsed during the first delay period is subtracted from thesecond delay period.
 8. A valve actuator control device as claimed inclaim 1 in which the desired position is set via a control meansaccessible by an operator of the valve actuator, and/or an activepressure monitoring means downstream of a flow valve which is controlledby said actuator.
 9. A valve actuator control device as claimed in claim1 in which a potentiometer connected to a valve stem extending from theflow valve provides the actuator position to the control device.